Several members of the protein kinase family have been clearly implicated in the pathogenesis of various proliferative and myeloproliferative diseases and thus represent important targets for treatment of these diseases. Some of the proliferative diseases relevant to this invention include cancer, rheumatoid arthritis, atherosclerosis, and retinopathies. Important examples of kinases which have been shown to cause or contribute to the pathogenesis of these diseases include c-ABL kinase and the oncogenic fusion protein BCR-ABL kinase, c-KIT kinase, c-MET, FGFR kinase family, PDGF receptor kinase, VEGF receptor kinases, FLT kinase family, the HER family and the cFMS kinase family. When such kinases are implicated in human disease, a kinase may present as an amplified kinase (i.e. overexpression of HER1 or HER2), a mutated kinase (i.e. c-KIT D816V) or an aberrant fusion protein (i.e. BCR-ABL).
c-KIT (KIT, CD117, stem cell factor receptor) is a 145 kDa transmembrane tyrosine kinase protein that acts as a type-III receptor (Pereira et al. J Carcin. (2005), 4: 19). The c-KIT proto-oncogene, located on chromosome 4q11-21, encodes the c-KIT receptor, whose ligand is the stem cell factor (SCF, steel factor, kit ligand, mast cell growth factor, Morstyn G, et al. Oncology (1994) 51(2):205; Yarden Y, et al. Embo J (1987) 6(11):3341). The receptor has tyrosine-protein kinase activity and binding of the ligands leads to the autophosphorylation of KIT and its association with substrates such as phosphatidylinositol 3-kinase (PI3K). Tyrosine phosphorylation by protein tyrosine kinases is of particular importance in cellular signalling and can mediate signals for major cellular processes, such as proliferation, survival, differentiation, apoptosis, attachment, invasiveness and migration. Defects in KIT are a cause of piebaldism, an autosomal dominant genetic developmental abnormality of pigmentation characterized by congenital patches of white skin and hair that lack melanocytes. Gain-of-function mutations of the c-KIT gene and the expression of phosphorylated KIT are found in most gastrointestinal stromal tumors and mastocytosis. Further, almost all gonadal seminomas/dysgerminomas exhibit KIT membranous staining, and several reports have clarified that some (10-25%) have a c-KIT gene mutation (Sakuma, Y. et al. Cancer Sci (2004) 95(9): 716). KIT defects have also been associated with testicular tumors including germ cell tumors (GCT) and testicular germ cell tumors (TGCT).
The role of c-KIT expression has been studied in hematologic and solid tumours, such as acute leukemias (Cortes J. et al. Cancer (2003) 97(11): 2760) and gastrointestinal stromal tumors (GIST, Fletcher J. et al. Hum Pathol (2002) 33(5): 459). The clinical importance of c-KIT expression in malignant tumors relies on studies with Gleevec® (imatinib mesylate, STI571, Novartis Pharma AG Basel, Switzerland) that specifically inhibits tyrosine kinase receptors (Lefevre G. et al. J Biol Chem (2004) 279(30): 31769). Moreover, a clinically relevant breakthrough has been the finding of anti-tumor effects of this compound in GIST, a group of tumors regarded as being generally resistant to conventional chemotherapy (de Silva C M, Reid R Pathol Oncol Res (2003) 9(1): 13-19). GIST most often become Gleevec resistant and molecularly targeted small therapies that target c-KIT secondary mutations remain elusive.
c-MET is a unique receptor tyrosine kinase (RTK) located on chromosome 7p and activated via its natural ligand hepatocyte growth factor. c-MET is found mutated in a variety of solid tumors (Ma P. C. et al. Cancer Metastasis (2003) 22: 309). Mutations in the tyrosine kinase domain are associated with hereditary papillary renal cell carcinomas (Schmidt L et al. Nat. Genet. (1997) 16: 68; Schmidt L, et al. Oncogene (1999) 18: 2343), whereas mutations in the sema and juxtamembrane domains are often found in small cell lung cancers (Ma P. C. et al. Cancer Res (2003) 63: 6272). Many activating mutations are also found in breast cancers (Nakopoulou et al. Histopath (2000) 36(4): 313). The panoply of tumor types for which c-MET mediated growth has been implicated suggests this is a target ideally suited for modulation by specific c-MET small molecule inhibitors.
The TPR-MET oncogene is a transforming variant of the c-MET RTK and was initially identified after treatment of a human osteogenic sarcoma cell line transformed by the chemical carcinogen N-methyl-N′-nitro-N-nitrosoguanidine (Park M. et al. Cell (1986) 45: 895). The TPR-MET fusion oncoprotein is the result of a chromosomal translocation, placing the TPR3 locus on chromosome 1 upstream of a portion of the c-MET gene on chromosome 7 encoding only for the cytoplasmic region. Studies suggest that TPR-MET is detectable in experimental cancers (e.g. Yu J. et al. Cancer (2000) 88: 1801). Dimerization of the Mr65,000 TPR-MET oncoprotein through a leucine zipper motif encoded by TPR leads to constitutive activation of the c-MET kinase (Zhen Z. et al. Oncogene (1994) 9: 1691). TPR-MET activates wild-type c-MET RTK and can activate crucial cellular growth pathways, including the Ras pathway (Aklilu F. et al. Am J Physiol (1996) 271: E277) and the phosphatidylinositol 3-kinase (PI3K)/AKT pathway (Ponzetto C. et al. Mol Cell Biol (1993) 13: 4600). Conversely, in contrast to c-MET RTK, TPR-MET is ligand independent, lacks the CBL-like SH2 domain binding site in the juxtamembrane region in c-MET, and is mainly cytoplasmic. c-MET immunohistochemical expression seems to be associated with abnormal β-catenin expression, a hallmark feature of epithelial to mesynchemal transition (EMT) and provides good prognostic and predictive factors in breast cancer patients.
The majority of small molecule kinase inhibitors that have been reported have been shown to bind in one of three ways. Most of the reported inhibitors interact with the ATP binding domain of the active site and exert their effects by competing with ATP for occupancy. Other inhibitors have been shown to bind to a separate hydrophobic region of the protein known as the “DFG-in-conformation” pocket wherein such a binding mode by the inhibitor causes the kinase to adopt the “DFG-out” conformation, and still others have been shown to bind to both the ATP domain and the “DFG-in-conformation” pocket again causing the kinase to adopt the “DGF-out” conformation. Examples that induce the kinase to adopt the “DGF-out” conformation can be found in Lowinger et al, Current Pharmaceutical Design (2002) 8: 2269; Dumas, J. et al., Current Opinion in Drug Discovery & Development (2004) 7: 600; Dumas, J. et al, WO 2003068223 A1 (2003); Dumas, J., et al, WO 9932455 A1 (1999), and Wan, P. T. C., et al, Cell (2004) 116: 855.
Physiologically, kinases are regulated by a common activation/deactivation mechanism wherein a specific activation loop sequence of the kinase protein binds into a specific pocket on the same protein which is referred to as the switch control pocket. Such binding occurs when specific amino acid residues of the activation loop are modified for example by phosphorylation, oxidation, or nitrosylation. The binding of the activation loop into the switch pocket results in a conformational change of the protein into its active form (Huse, M. and Kuriyan, J. Cell (2002) 109: 275).